Explicitly bounded comparison of floating point numbers.
Comparing floating point values for equality is really hard. To get it right requires careful thought and iteration based on the needs of each specific algorithm's inputs and error margins. This API provides a toolbox of components to make your options clear and your choices explicit to future maintainers.
Given how widely algorithmic requirements can vary, float_eq explores the
idea that there are no generally sensible default margins for comparisons.
This is in contrast to the approach taken by many existing crates, which often
provide default epsilon values in checks or implicitly favour particular
algorithms. The author's hope is that by exposing the inherent complexity in
a uniform way, programmers will find it easier to develop an intuition for how
to write effective comparisons. The trade-off is that each individual
comparison requires more iteration time and thought.
And yes, this is yet another crate built on the principles described in that Random ASCII [floating point comparison] article, which is highly recommended background reading 🙂.
Add this to your cargo.toml:
[dependencies]
float_eq = "0.2"
and, if you're using the 2015 edition, this to your crate root:
rust
extern crate float_eq;
then, you can import items with use:
rust
use float_eq::{assert_float_eq, float_eq};
This crate provides boolean comparison operations:
```rust assert!(floateq!(1000.0f32, 1000.0002, ulps <= 4));
// f32::EPSILON.sqrt() const ROUNDINGERROR: f32 = 0.00034526698; assert!(floatne!(4.0f32, 4.1, rel <= ROUNDINGERROR)); ```
And asserts:
```rust // 1.5 * 2f32.powi(-12), as per SSE intrinsics documentation const RECIPRELEPSILON: f32 = 0.00036621094; let recip = 0.1f32.recip(); assertfloateq!(recip, 10.0, rel <= RECIPRELEPSILON);
assertfloatne!(0.0_f32, 0.0001, abs <= 0.00005, ulps <= 4); ```
Arrays of compatible types are also supported, from size 0 to 32 (inclusive):
rust
assert_float_eq!([1.0000001_f32, 2.0], [1.0, 2.0], ulps <= 1);
See the [API documentation] for a long form introduction to the different kinds
of checks, their uses and limitations. Comparison of new types is supported by
implementing the FloatEq trait. Asserts may be supported by implementing the
FloatDiff and FloatEqDebug traits as well, which provide additional context
when debugging.
This crate can be used without the standard library (#![no_std]) by disabling
the default std feature. Use this in Cargo.toml:
[dependencies.float_eq]
version = "0.2"
default-features = false
Other optional features:
- num — implements FloatEq, FloatEqDebug and FloatDiff for
num::Complex where it is instanced with a compatible type.
The [approx], [float-cmp] and [almost] crates all provide a similar style
of general comparison operations, whereas [assert_float_eq] focuses
specifically on assertions. In contrast, [efloat] takes the approach of
tracking the error bounds of values as operations are applied.
Constructive feedback, suggestions and contributions welcomed, please [open an issue].
Release information is available in CHANGELOG.md.
Investigate whether the epsilon types should be generic parameters as opposed to associated types. It feels like composite types may sometimes want to be compared using a global bound and sometimes on a per-component basis, especially if they are composed of heterogeneous types.
#[derive] support for comparison of custom types that are composed of
already comparable floating point values.
Further support for basic Rust language components like tuples and containers
of compatible types like Vec, likely using PartialEq's support as a guide.
Investigate the safety guarantees of the ulps check. Currently, it doesn't act like the default floating point checks when it comes to NaNs and other special values.
More exhaustive testing. Tests currently cover all basic functionality, but there are lots of edge cases that aren't being tested yet.
Benchmark performance, especially the implications of chaining multiple tests.